1. The Field of the Invention
The present invention relates to a vascular endoprosthesis deliverable and deployable within a body vessel of a human or animal. More particularly, the invention relates to an interconnected segmented vascular endoprosthesis that includes decoupleable segments.
2. The Relevant Technology
Stents, grafts, and a variety of other endoprostheses are used in interventional procedures, such as for treating aneurysms, for lining or repairing vessel walls, for filtering or controlling fluid flow, and for expanding or scaffolding occluded or collapsed vessels. Such endoprostheses may be delivered and used in virtually any accessible body lumen of a human or animal, and may be deployed by any of a variety of recognized means. One recognized use for a vascular endoprosthesis is for the treatment of atherosclerotic stenosis in blood vessels. For example, after a patient undergoes a percutaneous transluminal coronary angioplasty or similar interventional procedure, a stent is often deployed at the treatment site to improve the results of the medical procedure and reduce the likelihood of restenosis.
To reduce the likelihood of restenosis, the stent may be configured to scaffold or support the treated blood vessel; if desired, the stent may also be loaded with a beneficial agent so as to act as a delivery platform to reduce restenosis or the like. Other suitable examples of medical conditions for which endoprostheses are an appropriate treatment include, but are not limited to, arterial aneurysms, venous aneurysms, coronary artery disease, peripheral artery disease, peripheral venous disease, chronic limb ischemia, blockage or occlusion of the bile duct, esophageal disease or blockage, defects or disease of the colon, tracheal disease or defect, blockage of the large bronchi, blockage or occlusion of the ureter, or blockage or occlusion of the urethra.
Some conventional stent designs may include a series of annular segments that may be connected in series by way of coupling elements. Typically, a vascular endoprosthesis, such as a stent, is delivered by a delivery sheath, such as a catheter, to a desired location or deployment site inside a body lumen of a vessel or other tubular organ. The intended deployment site may be difficult to access by a physician and often involves moving the delivery system through a tortuous luminal pathway that may involve various turns or curves. Thus, to allow advancement through the luminal pathway to the deployment site, a vascular endoprosthesis may need to flex or otherwise bend to traverse the various curves.
While flexing or bending during delivery to the deployment site, large axial or radial forces may be exerted on the vascular endoprosthesis. In order to withstand the forces exerted on the vascular endoprosthesis, the series of annular segments may be coupled together, thus providing additional support to the annular segments, which may help avoid a segment collapse or damage.
Once deployed, however, the coupling elements, in some applications, may be disadvantageous. For example, a vascular endoprosthesis deployed in a Superficial Femoral Artery (SFA) application undergoes longitudinal, bending, torsional, tensile and radial cyclical loading that may lead to fatigue failures in the segments after deployment. In particular, when the vascular endoprosthesis is forced to bend after being deployed, the coupling elements require the portions of the segment apposed to the outside of the curve to lengthen and the portions of the segment apposed to the inside of the curve to shorten.
Due to the fact that the segment may not expand evenly, the lengthening and shortening of the segments generally increases fatigue failures within the segments and/or the coupling elements. Current vascular endoprosthesis designs which are subjected to these forces often fail. Failure may result in crack formation and possible stent fracture. In the event of stent fracture, the sharp edges may puncture the vessel, muscle tissue, and/or cause bleeding. Consequently, the fractured stent may cause thrombus formation or blockage within the vessel.
One way to design a vascular endoprosthesis that is capable of withstanding the in vivo conditions after deployment is to not couple the annular segments of a vascular endoprosthesis together. This approach may, however, lead to difficulties with deploying the vascular endoprosthesis and create incomplete scaffolding. For example, during deployment, uncoupled annular segments may “jump” out of the delivery sheath in a way that creates an overly large gap between annular elements. A large gap between adjacent annular segments may result in insufficient vessel scaffolding. Moreover, due to the possibility that an uncoupled segment may “jump” out of the delivery sheath during deployment, the uncoupled segment may not interface with the body lumen wall in an effective way, again causing insufficient vessel scaffolding.